Thermodynamic analysis of chemical states of fission products in uranium-zirconium hydride fuel

The chemical state of fission products (FPs) in U + ZrH1.60 fuel was studie d from the thermodynamic point of view. Twenty most abundant FP elements we re taken into account in the system of U-Zr-H-O-FP in which oxygen is treat ed as an impurity. The Thermo-Gale computer code was used to calculate the equilibrium state of the multi-phase and multi-component system. This calcu lation shows that yttrium, the alkaline earth metals (Ba, Sr) and most of t he lanthanides prefer to form corresponding binary hydrides. Oxygen impurit ies in the system are likely to form a mixture of Y2O3, Pr-2 O-3. Sm2O3 as well as Ce2O3 depending on their fission yields. With increasing of burn-up , only a slight decrease of the hydrogen potential in the fuel pin can be e xpected because of the very little consumption of hydrogen in the hydrogena tion process of the FP. In the gas phase, H-2, Cs, Rb, CsRb as well as CsI are the main vapor species apart from the noble gases Xe and Kr. Solid swel ling of the fuel due to formation of condensed phases was calculated as a f unction of burn-up. (C) 2001 Elsevier Science B.V. All rights reserved.